Process for the recovery of the phosphorus content of phosphatic material



J. N. CABOTHERS.

PROCESS FOR THE RECOVERY OF THE PHOSPHORUS CONTENT OF PHOSPHATIC MATERIAL.

AP-PLICATTDN FILED MAR.I1,1920- RENEWED APR. 25. 1921.

z wfigg Patented Mar. 28, 1922 Tl||w w j Z V E ii is F I I T 0 ATTORNEY entree stares ALAB PATENT @FFHCEE.

AMA, ASEIGNOR TD FEDERAL PHOSPHORUS AMA, A CORPORATION OF ALABAMA.

PROCESS FOR THE RECOVERY OF THE PHOSPI-IORUS CONTENT OF PHOSPHATIC MATERIAL.

i alas-5o;

T 0 all whom it may concern:

Be it known that I, JoHN N. CARoTHEns, a citizen of the United States of America, residing at Anniston, in the county of Calhoun and .State of Alabama, have inventedcertain new and useful Improvements in Processes for the Recovery of the Phosphorus Content of Phosphatic Material, of which the following is a specification.

In the Journal of Industrial and Engineering Chemistry, Vol. X, No. 1, page 35, January, 1918, I have described experimental work done on a commercial scale in the manufacture of phosphoric acid. I have since made modifications and improvements upon the process therein described and referred to, which are the subject of the present application.

These modifications and improvements are of such importance as to transform the process referred to in said publication from one commercially unavailable because unprofitable, into one of commercial value and tbsthis end such modifications and improvelncnts extend both to the material treated and the control of the operation; thus enabling the operator to regulate with substantial accuracy the composition and purity of the phosphoric acid product as well as to reduce the waste of the phosphorus content of the rock to a minimum.

In the process referred to in said publication, whatever phosphorus failed to be volatilized from the slag was a total loss because non-recoverable from the slag, whereas in my present process a large proportion thereof is recovered from the slag as commercially valuable ferro-phosphorus. Moreover in the process referred to in said publication the phosphorus volatilized from the slag in being transformed and isolated as phosphoric acid, was substantially uncontrollable with respect to its ultimate composition and purity, whereas, by my present process I am enabled to determlne 1n advance whether the phosphoric acid product shall be meta, pyro orortho and that it shall be so pure as to be even available for food Specification of Letters Patent.

Patented Mar. 28, 1922.

Renewed April 25, 1921. Serial No. 464,258.

that it shall be the handling of a minimum or medicinal purposes and produced by volume of gas.

lVith processes which have been suggested for the production of ferro-phosphorus serious difficulties arise when such an operation s attempted on a commercial basis, as for 1nstance:

1. Regardless of theoretical considera tions, it has been proven by actual operation under my observation that, notvvithstandimg, the employment of the best skill in electric furnace and metallurgical control and regulation, a large percentag of the phosphorus charged will be evolved and lost with the furnace gases, as only a part of the phosphorus charged can be alloyed with the iron to produce a commercial grade of ferrophosphorus.

2. The said evolved phosphorus bearing fumes are so noxious and objectionable that continued operation is impossible on account of their :.disagreea.ble effect on worlnncn. (their destructive effect upon the electrical and mechanical appliances necessary for the operation of the furnace) and because of the nuisance to 3. The low recovery of the phosphorus in the production of the iron phosphorus alloy (ferro-phosphorus) of commercial grade by the electric smelting process in such that. due tothe waste fumes and inefiiciency of the process, without the collection of phos-' phorus bearing gases so evolved, it is not commercial, besides such process is a profligate waste of natural and national resources.

Many attempts have been made, and numerous processes proposed, to smelt natural phosphates with sufficient acid flux to combine with the bases of the phosphates, and with coke to reduce the phosphorus contained in said phosphates both in fuel fired and electric furnaces, thereby volatilizing a portion of the contained phosphorus in the phosphates, and then to oxidize the evolved phosphorus to phosphorus pentoxide and absorb it in water. It is significant that none of these processes for the production the surrounding community.

of phosphoric acid, so far as I have been able to ascertain, have been continued beyond the experimental stage.

My own investigations have led me to believe that the smelting of phosphate rock and coke as heretofore practiced in an electric furnace is of doubtful commercial value when conducted for the sole purpose of producing phosphoric acid.

My invention contemplates the joint production in an electric furnace of phosphoric acid and ferro-phosphorus in such manner as to make the operation both practicable and commercially feasible. 'In order that my invention may be fully understood and distinguished from existing processes, the steps in my process may be outlined as follows:

I charge into an electric furnace the following mixture:

(a) Iron bearing materials, containing a definite quantity of iron;

(2)) Phosphate rock; (natural tricalcic phosphate) in'such proportion of phosphorus content to that of the weight of the iron in the charge, as will in practice produce the desired iron-phosphorus alloy;

(0) Carbon; in suflicient quantity to reduce the phosphorus from the phosphate rock of the charge;

(d) Sand or other acid flux in such quantity as will combine with the lime and other bases of the phosphate rock, andsuch other bases as exist in the charge, to form compounds of desired fluidity and simultaneously to form a slag of required acidity to I liberate the phosphorus.

The phosphorus liberated within'the heated reacting mass of the above charge in the electric furnace operation is finely divided elemental phosphorus and as such is either all'oy'ed with the iron or passes up through the descending column of charge in the furnace, with the other gases, principally car bon monoxide. If all air were excluded from the interior of the furnace, the phosphorus and carbon monoxide would remain as such, and accordingly elemental phosphorus might be collected by properly condensing the gases. In the case of my process, suflicient oxygen as air is admitted to oxidize the carbon monoxide to carbon dioxide, and the phosphorus to phosphorus pentoxide. This phosphorus pentoxide is present'as suspended particles in the accompanying gases, thus existing in the state of a fume and due to this fact it occupies a relatively small volume when compared to the accompanying gases. Tests have been made on various methods of collecting this fume, and I find that it will pass through many ordinary filtering mediums and chemical reacting compounds, even strong alkali.

I have discovered that as the temperature of this gas and fume mixture passes through certain definite ranges, the phosphorus pentoxide absorbs from the surrounding gases a definite quantity of Water, and combining with such water forms successively in ascale of lowering temperature, meta, pyro an ortho-phosphoric acid. This reaction probably proceeds with considerable velocity because of the fineness of the phosphorus pentoxide particle, its relatively small volume as compared with the associated gases, and the peculiar ailinity of the phosphorus pentoxide for varying proportions of water within definite ranges of temperature.

In the treatment of the evolved gasesl propose to regulate and control- (a) the degree of oxidation of the gases evolved from above described furnace charge by analysis of the gases;

(b) the temperature of the gases b water or air cooling externally or internally; and

(c) the velocity of the gases by regulation of an exhaust fan or equivalent means.

" The velocity of the gases may not be definitely specified, because ofthe variations resulting from varying factors, but in my practice analyses of the gases are made to determine when the exact proportion of the oxygen has been drawn into the furnace to combine with the gases to convert the hosphorus into phosphorus pentoxide and the carbon monoxide into carbon dioxide, as it is my purpose to admit only sufiic'ient oxygen to make sure of the requisite degree of oxida-' tion of the furnace gases. 1 find that oxidation of the gases is facilitated by allowing the gases-to remain for a short time within the furnace in a relatively quiet state, so that practically no oxidation takes place after the gas and fume mixture leaves the furnace proper or the combustion chamber. 1 have also found by regulating the velocity of the gas and fume mixture, as previously referred to, I am able to produce an acid of higher purity than heretofore believed pos sible.

After the gas and fume mixture are removed from the furnace, they are .cooled in any suitable manner to the predetermined temperature at which. the phosphorus pentoxide absorbs the requisite quantity of water to. produce the meta, yro or orthophosphoric acid of the desired concentration. The gases and fumes after being thus oxidized, cooled and hydrated, are passed through an electric precipitator, as a preferred means, to precipitate the phosphorus in the form of the desired phosphoric acid and of. the desired concentration.

I have thus discovered that by the ex-.

ercising of the control of the temperature of the gas and fume mixture, the degree of hydration of the phosphoric pentoxide by the water vapor accompanying the gases, is

. sired and in all cases .I have Y from the charge,

pyro-phosphoric acid and collected in of ortho-phosphoric acid.

.As illustrative of this feature of my process, where the evolved gases are reduced to a temperature of approximately 350 C. meta-phosphoric acid is produced according to the formula By further reducing the temperature to approximately 215 C. pyro-phosphoric acid will be producedaccording to the formula By further reducing the temperature of the gases to approximately 210 (1., pure ortho-phosphoric acid is produced according to the formula By further reducing the temperature the phosphoric acid will absorb additional water from the vapor in the gases and thus the desired dilution of ortho-phosphoric acid can be produced, the acid percentage varying with the'temperature of the gas and fume mixture and in like manner throughout the whole range of temperature for the gases, varying grades, mixtures and dilutions of phosphoric acid may be produced as defound that the necessary water for combining with the gases is obtainable from the atmosphere, or from internal cooling Water. Water may be admitted to cool the gasesland at the temperatures at which the gas is'subsequently treated, it exists as va-' por, and will be taken up and combined with the phosphorus pentoxide forming meta, pyro or ortho-phosphoric acid, as above described.

A decided advantage in the above described process is that a complicated step is eliminated in that T find it unnecessary to subject the gas and fume mixture to successive electrical field strengths, but am able to collect an acid directly which is of high purity.

The phosphoric acid I produce is adapt ed for any of the well known uses and par-' ticularly in foods and medicine where an acid of high purity is required, with special reference to arsenic and lead compounds.

- Furthermore, because of my ability to produce an acid of highconcentration, it is better adapted to shipment that the ordinary acid-produced by the treatment of phosphate rock with sulfuric acid, because of the concentration necessary in the case of this latter mentioned process Moreover, pyro and meta-phosphoric acid cannot be method, except by prolonged heating, whereas, in the case of my process I producepyro or meta-phosphoric acid as conveniently as any concentration of ortho-phosphoric acid.

As illustrative of a typical apparatus for carrying my process into effect, reference is, made to the accompanying drawings, in which I An electrical furnace 1 of any standard type is shown, having the electrodes 2 entering at the top and having atap hole 3. The stock is charged in any suitable manner, as through a door 4, from the upper charging floor level 5 and the evolved gases are drawn off from the hood 6 covering the top of the furnace and conducted through a pipe 7 undera cooling spray 8, and thence delivered through a pipe 9 to an exhaust fan 10 which moves the gases at the velocity desired and discharges them into the header 11 of an electrical precipitator com prising terra cotta pipes 12 in which-are suspended insulated electrodes 13, the pipes being grounded by a wire 14 and the precipitated phosphoric acid being drawn off by a spout l5 and delivered to any suitable collecting vessel or storage tank. All of the pipes, as well as the exhaust fan, are of suitable material to resist the actionof the gases.

I prefer to conduct my process in this apparatus as follows:

A normal charging mixture may be approximately 500 lbs. ofcrushed phosphate rock analyzing 14% phosphorus, 200 lbs. of cast iron borings, 135 lbs. of'sand and 95 lbs. of coke. These proportions will vary widely depending on the analysis of the phosphate rock. This mixture is introduced through the door 4, up to about the level of the lower ends of the electrodes. Then a comparatively small quantity (e. g. less than 1,000 lbs.) of a mixture somewhat richer in carbon is introduced around and between the electrodes to facilitate the passage of the current in starting. Then the current is turned on graduallyand when it reaches about 1,000 K. "W. slag will begin to form between the electrodes which continues to conduct the current as the slag volume increases and as the current builds up. The charging is continued and kept up to about the level of the floor 5, and the current builds up to about 2,000 K. W. and the process is substantially continuous. The slag basin in normaloperation comprisesthe bottom of the furnace up to about the level of the lower ends of the electrodes.

The ferro-phosphorus is drawn off through the tap hole 3, with the slag from which it is subsequently separated.

The gases escaping from the slag pass up through the solid material into the furnace chamber above the same, where they mingle with air drawn by the fan through the door 4. The amount of air may be regulated by the opening and closing of the door and the tion of the passage velocity of the fan. This chamber is of such size as to afford the gases a period of comparative rest before being drawn into the passage 7. This rest period gives the gases time to take up the desired quantity of oxygen from the air before substantial cooling or hydration takes place, the supply of air being regulated so that there is substantially no excess of oxygen. The desired degree of oxidation is thus substantially complete before the gases leave the furnace the electric precipitator wherein the carbon dioxide and nitrogen are removed and the phosphoric acid (either meta, pyro or ortho, as desired) is collected substantially pure.

In obtaining the pure product of regulated composition and also in reducing to a minimum the waste of the phosphorus content of the ore, substantially all of the above steps co-operate. Thus any phosphorus whichby design or otherwise is not volatilized by the furnace is, in a large proportion seized by the iron and converted into valuable ferro-phosphorus, while the substantial completion of the oxidation of both the volatilized phosphorus and carbon monoxide is insured by the rest period within the furnace before hydration and the regulation of the air supply to obviate any substantial ex-- cess ofoxygen as well as the separation of the dust causes the gasesto be presented to the electric precipitator in a condition wherein their volume is at a minimum and-wherein there is substantially no content to be precipitated as an impurity with the phosphoric acid. In co-operation with this is the fact that it lies within the power of the operator to determine in advance what shall be the com osition of the phosphoric acid produced. aving thus described my invention, what Tclaim as new and desire to secure by Letters Patent, is a 1. The process of obtaining an approximately quantitative utilization of phorus content of phosphatic material, which consists in expelling the phosphorus from the phosphatic material in the presence of silicious and carbonaceous materials in an electric furnace and simultaneously presenting iron to one portion of said phosphorus and oxygen and moisture to another portion thereof, whereby apprpximately all of said the phos- I and oxygen and moisture to another port onv thereof, whereby approximately all of said phosphorus is converted into ferro-phosphorus and phosphoric acid, While regulating the degree of hydration of the phosphoric acid by regulating the temperature of the oxidized phosphorus in contact with the moisture.

3. The process for producing phosphoric acid in an electric furnace, which consists in charging the furnace with phosphatic, silicious and carbonaceous materials in suitable proportions, collecting the evolved phos phorus bearing fumes with the furnace gases, controlling the oxidation, the reduction in temperature and the hydration of said fumes in said gases according to the grade of phosphoric aciddesired, and electrically precipitating thephosphoric acid from said gases.

4. The process of producing phosphoric acid in an electric furnace, which consists in regulating the degree of oxidation of the gases evolved in the furnace, the temperature of said gases and the velocity of said gases, then causing the phosphorus pentoxide in such gases to absorb and combine with such predetermined quantity of water as will produce a predetermined concentration of phosphoric acid, and subjecting said gases to an electrical field adapted to collect substantially all the phosphorus bearing fumes evolved from said furnace operation in the form of phosphoric acid, as described.

The hereindescribed process for the joint production commercially of ferrophosphorus and phosphoric acid and the elimination of noxious fumes, which consists in charging an electrical furnace with iron, natural phosphate, silicious flux and'carbon, controlling the oxidation of the evolved gases and their velocity of flow and temperature according to the phosphoric acid desired, treating the gases to collect the Suspended phosphorus as phosphoric acid and tapping the ferro-phosphorus and slag from the furnace. i

6. The hereindescribed process for the joint production commercially of ferrophosphorus and phosphoric acid and the elimination of noxious fumes, which consists in charging an electrical furnace with iron, natural phosphate, silicious flux and carbon, oxidizing the gases while moving at a low velocity, removing the same from the furjoint production commercially phoric acid and tapping the ferro-phosphorus from the furnace.

7. The hereindescribed process for the of ferro-phosphorus and phosphoric acid and the slim ination of noxious fumes, which consists in charging an electrical furnace with iron, natural phosphate, silicious flux and carbon, oxidizing the gases Within the furnace, reducing the temperature of the gases in the presence of moisture, causing the compounds to ,absorb a predetermined quantity of water, subjecting said compounds to the action of an electrical field, precipitating the .suspended phosphorus compounds from the gases as phosphoric acid, and tapping the ferro-phosphorus from the furnace.

8. The hereindescribed process for the joint production commercially of ferrophosphorus and phosphoric acid and the elimination of noxious fumes, which consists in charging an electrical furnace With iron, natural phosphate, silicious flux and carbon, oxidizing the furnace gases at a low velocity, reducing the temperature of said gases to form the desired grade of phosphoric acid, causing the phosphorus compounds to absorb a predetermined quantity of water, subjecting said compounds and furnace gases to the action of an electrical field, precipitating the suspended phosphorus compounds as meta, pyro or ortho-phosphoric acid, or cornounds or dilutions thereof accordin' to the temperature to which the gases are reduced, and tapping the ferro-phosphorus from the furnace.

9. The hereindescribed process for .the-

joint production commercially of ferrophosphorus and phosphoric acid and the elimination of noxious fumes, which consists in'charging an electrical furnace with iron, natural phosphate, silicious fiux and carbon, oxidizing the gases, reducing the ten1- perature of said gases to form the desired grade of-phosphoric acid, causing the phosphorus compounds to absorb from the atmosphere supplied to the furnace and from the stock a predetermined quantity of water, subjecting said compoundsand furnace gases to the action of an electrical field, precipitating the suspended phosphorus compounds .f

as meta, pyro or ortho-phosphoric acid, or compounds or dilutions to t e temperature to reduced, and tapping from the furnace. I

10. The hereindescribed, process for the joint production commercially of ferrophosphorus and phosphoric acid and the elimination of noxious fumes, which consists in charging an electrical furnace with iron,

which the gases are the farm-phosphorus thereof, according natural phosphate, silicious fiuz: and carbon, oxidizing the gases, reducing the temperature of said gases to from 90 to 120 (l, causing the phosphorus compounds to absorb a predetermined quantity of water, subjecting said phosphorus compounds and furnace gases to the action of an electrical field, precipitating the suspended phosphorus compounds from the gases as to ortho-phosphoric acid, and tapping the ferro-phosphorus from the furnace.

11. The hereindescribed process for the joint production commercially of ferrophosphorus and phosphoric acid and the elimination of noxious fumes, which consists in charging an electrical furnace with iron, natural phosphate, silicious flux and carbon, oxidizing the gases, reducing the temperature of said gases to from 120 to 210 G, causing the phosphorus compounds to absorb a predetermined quantity of water, subjecting said phosphorus compounds and furnace gases to the action of an elecin chargingan electrical furnace with iron,-

natural phosphate, silicious flux and carbon, oxidizing the gases, reducing the temperature of said gases to from 210 to 815 causing the phosphorus compounds to absorb a predetermined quantity of water, subjecting said phosphoruscompounds' and furnace gases to the action of an electrical field, precipitating the suspended phosphorus compounds from the gases as pyrophosphoric acid, and tapping the ferrophosphorus from the furnace.

13. The hereindescribed process for the joint production commercially of ferrophosphorus and phosphoric acid and the elimination of noxious fumes, which consists in charging an electrical furnace with iron, natural phosphate, silicious flux and carbon, oxidizing the gases, reducing the temperature of said gases to from 315 to 100 (1, causing the phosphorus compounds to absorba predetermined quantity of water, subjecting said phosphorus compounds and urnace gases to the action of an electrical field, precipitating the suspended phosphorus compounds from the gases as metaphosphoric acid, and tapping the ferrophosphorus from the furnace.

14. The process of obtaining ferro-phosphorus and phosphoric acid, which consists in charging an electrical furnace with iron, natural phosphate, silicious flux and carbon, oxidizing and hydrating the gases, separating the dust therefrom, and forcing the same through an electric separator While tapping 'the ferro-phosphorus from the furnace.

15. The process for producing phosphoric acid 1n an electriefurnace, whlch consists in charging the furnace with phosphatlc,

silicious and carbonaceous materials in su1table proportions, collecting the evolved phosphorus bearing fumes with the furnace gases, controlling the oxidation, the reduclatoeeo JOHN N. CAROTHERS.

Witness THEODORE SWANN. v 

